Device for the positionally exact synchronization of the parallel course of recording medium webs in an electrographic printer device

ABSTRACT

A printer for printing endless paper webs on both sides has two printing stations with a web turnover station therebetween. The paper web is fed in parallel side-by-side to the two printing stations which are on the same rollers. The drive of the web through the printer is by a positive drive, using pins to engage holes in the paper web, for example, into the first printing station. The drive of the paper web thereafter is by friction drive to permit slippage in the drive to compensate for variations in paper length during heating, etc. The slippage is controlled by brakes or other drag inducing devices acting on one or both of the two portions of the paper web.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a device for the positionally exactsynchronization of the parallel course of recording medium webs in anelectrographic printer device.

2. Description of the Related Art

An electrographic printer device wherein two recording medium websarranged parallel are simultaneously moved through the printer andprinted is disclosed, for example, by published International Patentapplication WO 94/27193. In such a printer device and otherpaper-processing systems wherein two parallel paper webs pass throughsuccessive function units with friction or positive drive, the drive ofthe paper webs is a particular problem. In order to avoid malfunctions,thus, a parallel, synchronous paper course must be guaranteed.

DESCRIPTION OF THE PROBLEM

Generalities

The following is to be noted or, respectively, the following problemsgenerally occur when synchronously conveying a paper web through aplurality of function units of a printer device: In order to achieve aprescribed registration precision, the printing format must be alignedrelative to the paper form when printing.

Tensile forces occur in the web upon passage of the web through theprinter. These are partly unavoidable, for example due to friction. Onthe other hand, tensile forces are intentionally introduced into the webin order to stabilize the paper running.

The tensile forces in the paper vary during printing.

The drives drive the web opposite the influence of the tensile forces(described below).

The paper web shrinks when it is heated, namely dependent on the papergrade (which determines, for example, the water content) and the extentof heating. Upon passage through a standard type thermal fixing station,for example, the shrinkage in the web direction lies on the order ofmagnitude of 0.06%.

The advance feed holes of the paper webs are subject to manufacturingtolerances. These amount to up to 0.12% of the rated dimension.

DISCUSSION OF THE VARIOUS OPERATING MODES

Different conveying principles are applied for driving the paper webs,for example in continuous printers. These are:

Friction Drive

The drive of the paper webs by friction usually ensues in roller nips orvia friction roller drives. What is thereby particularly critical is thedrive in the roller nip (in other words, the fixing gap) between thefixing and pressure rollers of a thermal pressure fixing station.

A friction drive conveys a web length per a time interval. However, theslippage, which occurs on principle in any friction drive, variesdependent on force and friction relationships. Slippage means that thereis no fixed transmission ratio between the driving part and the drivenpart, and the driven part lags behind the driving part to a greater orlesser extent. Given drive in the roller nip of, for example, a fixingstation, the paper web is slower by the slippage than the surface speedof the drive roller. Given a constant drive motor speed, thus, the speedof the driven paper web changes due to influences of force and friction.

Positive Drive

The drive of paper webs by positive lock usually ensues viapaper-conveying caterpillars or pin wheels that engage into advance feedholes of the paper. What is meant here by a positive drive is also adrive that is in fact a friction drive in mechanical terms but iscontrolled, for example, by electronic means to the conveying of formelements. Such a drive, accordingly, automatically compensates fordiffering slippage and behaves like a positive drive with respect to theweb speed. Form elements are repeating, detectable features involvingthe paper web. These, for example, can be: advance feed holes, printingmarks, folds, perforations, or labels.

A positive drive conveys a defined plurality of form elements (forexample, links of a chain, or advance feed holes in the paper web) pertime interval. Due to various influences, the advance feed holes canhave different spacings from one another (due to perforation tolerances,or paper shrinkage). Tolerances in the hole spacing below an allowablelimit do not influence the function of the drive. The tolerancesoccurring here are on the order of magnitude of up to 0.2%. Whenconveying a specific plurality of advance feed holes, a respectivelydifferent web length is thereby conveyed.

Given a constant drive motor speed, thus, the speed of the driven paperweb varies due to perforation tolerances and temperature influences. Inelectrographic printer devices that work with continuous stock, the formposition is permanently defined relative to the advance feed holes. Theform synchronization is thus usually accomplished via the advance feedholes and a positive drive. The alignment of the printing formatrelative to the paper form in turn usually ensues via the form elementsin a positive drive.

A defined, constant paper speed can thus not be achieved with either ofthe two drive types solely by keeping the motor speed constant.

Two Drives in Sequence

When, in a paper-processing system, a plurality of drives aresequentially employed along a web, a corresponding synchronization mustensue dependent on the nature of the drives. FIGS. 1 through 3 showsseveral possibilities of the series circuit of web drives. The elementsshown as brakes symbolically illustrate the creation of the tensileforces in the paper. M is the drive moment of the respective drive, nbeing the drive speed.

Two Positive Drives in Sequence (see FIG. 1)

When, given the series connection of two positive drives, the two drives(speeds) are rigidly coupled to one another, the content of the webstore lying therebetween does not change summarily. When an advance feedhole is supplied from the 1^(st) drive, an advance feed hole is drawnoff from the 2^(nd) drive. The sum of advance feed holes between thedrives remains the same. No regulation of the web length between drive 1and 2 is thus required. The fixed coupling of drive 1 and 2 can ensueboth mechanically (for example, via a fixed shaft connection or agearing arrangement) as well as electronically (for example, byemploying two stepping motors operating by the same clock signal).However, the web speed, which changes with the perforation tolerance, isaffected by tolerances given this drive system.

Two Friction Drives in Sequence (see FIG. 2)

The coupling of the drives here does not assure disruption-free runningof the paper web. Dependent on the extent of the slippage of drives 1and 2, a difference in drive speed will thus arise in the running paper.This means a general error for the web store between the two drives. Theweb store is thus either emptied and the paper tears or it overflows. Aregulation of the web length between the two drives must thus ensuehere. The regulation is usually implemented as a regulation of the drivespeed of at least one of the two drives. Whereby the content of the webstore is kept at a constant value with the regulation of the drivespeed.

Two Different Drives in Sequence (see FIG. 3)

When two different drives are utilized in series, a control of the weblength between the two drives must again ensue. A coupling of the drivesis inadequate since the web speed in the positive drive fluctuates withthe perforation tolerance and fluctuates with the tensile forces in thefriction drive. These fluctuations do not compensate each other; ageneral error with the afore-mentioned consequences arises for the webstore.

Two Webs Synchronously Parallel

Given the problem described here, two paper webs are processedsynchronously in parallel. This is the case given: two completelyindependent webs that pass through the printer in parallel side-by-sideoverall or in sub-sections; one web that is returned in a loop and againtraverses in parallel drives after the return. (See FIG. 4).

What parallel means is that the webs runs next to one another, namelythrough the same divided or undivided aggregates or function units. Whatsynchronous means is that no shift occurs between the forms of the oneweb and the forms of the other web when the paper is running. In thepresent case, the leading edge of the forms is the same in both webswhen the alignment line has been reached. Here, the alignment linecoincides with the line in which the paper is printed. In order toguarantee the synchronism, a common positive drive is utilized here. TheA-web and B-web emerge in parallel from the coupled positive drive. Dueto differences in the advance feed holes, the paper web speeds of web Aand web B are different even though the exiting hole frequency is thesame.

In the illustrated case of FIG. 4, the A-web runs through the fixingroller pair after the caterpillar drive. The fixing roller pair is afriction drive, on the one hand; on the other hand, the printing formatis fixed to the paper here by hot rollers. The paper web shrinks in thelongitudinal direction given this heating. The spacing of the advancefeed holes thus shortens by, for example, approximately 0.6%. The A-webis in turn returned following the fixing rollers and then runs throughthe caterpillar drive as the B-web in parallel to the new A-web. Itfollows therefrom that the B-web now runs slower than the A-web by that0.06% shrinkage.

The problem thereby deriving is to process the two webs having differentspeeds with an undivided pair of fixing rollers wherein the surfacespeed of the drive friction roller cannot be differentiated for the twowebs.

A regulation of the drive speed as initially described is not adequatehere by itself since only one web can be regulated thereover between twodrives.

It must be additionally guaranteed in the illustrated arrangement ofFIG. 4 that the paper length does not summarily change in the returnloop between the A-web and B-web.

The synchronization of successive conveyor units for a single web in aweb-processing system, which is for example a continuous printer, canensues via a band store, for example a loop-forming unit. The conveyorspeeds of the adjoining drives are thereby regulated dependent on thestorage content thereof. For the described reasons, such asynchronization is not possible given a parallel-synchronous operationof two webs.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a devicefor the positionally exact synchronization of the parallel course ofrecording medium webs in an electrographic printer device, whereby therecording medium webs pass through a first function region in parallelside-by-side positively driven via a drive means and are then suppliedin parallel side by-side to a second function region with a frictiondrive.

A further goal of the invention is also to fashion the device such that,in particular, it enables a simple and dependable regulation of theparallel course of the recording medium webs in a electrographic printerdevice as disclosed by the published International Patent application WO94/27193.

These goals are fundamentally achieved by a control means that regulatesthe parallel running by controlling the slippage of the friction drive.

Advantageous embodiments of the invention are provided by a device asdescribed above whereby respective loop tractors with sensors acquiringtheir swivelled position are allocated to the recording medium webs.Loop-forming units that are fashioned such that they deflect therecording medium webs with an adjustable deflection force dependent ontheir rotated position are provided. The loop-forming units comprise adeflection element with appertaining deflection spring that engage atthe recording medium webs and are pivotable around a rotational axis,whereby the deflection spring is coupled to a tensing means for settingthe spring prestress.

As a further improvement, the above device has the regulating meanscomprising a first function group that controls the content of the bandstore that, for example by varying the speed of the friction drive,influences the content of the band stores of the recording medium websin the same sense, and also comprises a second function group thatcontrols the difference of the store contents of the band stores that,for example by varying the tensing force in the respective recordingmedium web, oppositely influences the content of the band stores.

Sensors for sensing markings on the recording medium webs may beprovided.

A brake that is arranged preceding the friction drive in the recordingmedium conveying direction and whose braking power on the recordingmedium web or webs can be regulated. The brake has a glide surfacecomprising suction openings accepting the recording medium webs which isallocated to each of the recording medium webs, the glide surface beingcoupled to a means generating an adjustable underpressure.

The device of one embodiment has a transfer printing region, a transferprinting station as the first function region and a fixing station asthe second function region.

The device of a preferred embodiment has a second function region thatcomprises a fixing drum with an appertaining pressure roller thatpresses the recording medium against the fixing drum, whereby at leastone of the rollers is heated and motor-driven. A controllable device forsetting the pressing power on the recording medium webs is provided.This has a movably seated pressure roller pressing the recording mediumwebs against a drive roller of the friction drive and having a forceadjustment mechanism coupled to the pressure roller in order toweb-specifically vary the pressing power of the pressure roller in theregion of the recording medium webs in one embodiment. Spring elementsthat are coupled to a setting means and to a respective lateral bearingelement of the pressure roller such that they press the pressure rollerin force-compensating fashion against the cooperating roller in a zeroposition of the setting means are preferred, whereby an transmission offorce to the bearing elements that is dependent on setting position thenensues by excursion of the setting means out of the zero position.

A means for the controllable variation of the coefficient of friction ofthe rollers may be provided. The variation of the coefficient offriction ensues by controlled delivery of parting oil.

The device described above has a fixing station that is fashioned as aflash fixing means in one printer embodiment. The fixing station isfashioned as a projector fixing means in another.

The invention provides that the device has means allocated to theregulating means via which a synchronization stop is triggered givenupward transgression of a predetermined range of control, during whichsynchronization stop a synchronization of the parallel running of therecording medium webs can ensue by relative displacement of therecording medium webs into a synchronous position.

An application of the transport system described is arranged in anelectrographic printer device for single-sided or both-sided printing ofa band-shaped recording medium, whereby the printer device comprises:

an intermediate carrier for generating toner images allocated to thefront side and/or the back side of the recording medium;

a transfer printing station having a first transfer printing region forthe transfer of a first toner image onto a front side region of therecording medium and a second transfer printing region lying there nextto for the transfer of a further toner image onto the front side regionor a back side region of the recording medium, as well as a conveyormeans that positively drives the recording medium in the transferprinting regions;

a fixing station following the transfer printing station in conveyingdirection of the recording medium having an allocated friction drive forthe recording medium, whereby the recording medium, in a first recordingmedium web proceeding from a delivery region, is conducted via the firsttransfer printing region to the fixing station and, turned over by aturning means as needed for printing the bask side region, is conductedtherefrom to the second transfer printing region and is conducted againthrough the fixing station in a second recording medium web.

The invention also provides a method for producing a disruption-freerunning of recording medium webs in an electrographic printer device,whereby the recording medium webs, positively driven in common via adrive means, pass through a first function region in parallelside-by-side and are then supplied in parallel side-by-side to a secondfunction region with common a friction drive, whereby the surface speedof the surface of the friction drive driving the webs cannot bedifferentiated for the webs, comprising the following steps:

acquiring the relative displacement in the conveying direction of therecording medium webs relative to one another in a region between thetransfer printing region and the fixing station;

controlling the slippage of the friction drive in the conveyingdirection of each individual recording medium web until the relativedisplacement falls below a prescribable value.

By collective and web-specific control, the size of the occurringslippage of each individual paper web is regulated such in the frictiondrive that a disruption-free paper running is guaranteed. To this end,the control can--during and outside of the printing mode--influence:

the speed of the friction drive,

the paper-tensing forces of the individual paper webs,

the surface pressing in the nip of the friction drive,

the coefficient of friction of the friction roller (via the lubricationthereof).

It also serves for:

controlling events during paper insertion, start and stop, acquiringerrors of the machine and of the paper running.

Each web has a web store between the positive drive and the frictiondrive, this also being referred to as band store. Therein, a respectiveloop-drawing unit tenses the paper web and measures the content of theweb store (i.e. the length of the paper loop).

The control is divided into two function groups that are largelyindependent of one another:

The Loop Length Control

The loop length control acts in the same sense on both paper loops. Themain instrument of this control is the speed of the friction roller(which is the fixing drum).

The Loop Difference Control

The loop difference control acts oppositely on the two paper loops.Here, the main instrument is the web-specific tension in the respectivepaper web.

The basic procedure of the control is to keep the paper loop length,i.e. the storage content of the band stores, within allowed limits.

Such a control via the slippage is unusual, particularly given theemployment of a friction drive in a fixing station, since a slippageusually results in a smearing of the toner image, which is preciselywhat should be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are shown in the drawings and are describedin greater detail below with reference to the drawings by way ofexample. Shown are:

FIG. 1 is a schematic illustration of a recording medium web with twopositive drives in series.

FIG. 2 is a schematic illustration of a recording medium web with twofriction drives in series.

FIG. 3 is a schematic illustration of a recording medium web with twodifferent drives in series.

FIG. 4 is a schematic illustration of the paper course in a printerdevice with two recording medium webs running in parallel.

FIG. 5 is a schematic illustration of the paper course in a printerdevice with duplex printing on a single paper web with two recordingmedium webs running in parallel.

FIG. 6 is a schematic illustration of the structure of a printer devicewith duplex printing according to FIG. 5 with a control means for thesynchronization of the recording medium webs running in parallel.

FIG. 7 is a schematic illustration of the function of a loop tractoremployed as a band store.

FIGS. 8-12 are schematic illustrations of loop tractor configurationswith adjustable excursion force and different force characteristics;

FIG. 13 is a schematic illustration of a pressing power adjustmentmechanism for the pressure roller of a fixing station; and

FIG. 14 is a perspective view of an electrographic printer device forprinting web-shaped recording media in duplex mode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is described below on the basis of the structure of anelectrographic printer device for one-sided or both-sided printing of aband-shaped recording medium as disclosed by the published InternationalPatent application WO 94/27193. The content of this publication isincorporated herein as part of the disclosure of the presentapplication. Paper course in an electrographic printer device withreturn of the recording medium and a parallel running control

According to the illustration of FIG. 5, the band-shaped recordingmedium 1 in the inventive printer device is drawn into the printer by,for example, a roller proceeding from a delivery region and, in theregion of the alignment line 2, is printed with toner images allocatedto the front side. The recording medium 1 is thereby fashioned ascontinuous fanfold stock. The transfer printing region for thetransfer-printing of the toner images from an intermediate carrier (suchas a photoconductive drum) onto the recording medium 1 having astructure according to the application WO 94/27193 is located in theregion of the alignment line 2. The drive 3 in the transfer printingregion ensues positively via tractors with nipples or pegs arrangedthereon that engage into corresponding margin perforations (shown aswhite voids) of the recording medium 1. For distinguishing the web thatis newly drawn in and allocated to the front side in the transferprinting region (alignment line 2), let the "front side web" be calledA-web (reference character 5) and the "back side web" be called B-web(reference character 4). The A-web 5 passes a band store in the form ofa loop tractor 6/1 and is driven by a friction drive 8 in the form of afixing station via an underpressure brake 7/1. Subsequently, the web isreturned, turned over in a turning means 10 and resupplied as the B-web4 to the positive drive 3 in parallel to the web that is newly drawn in.When passing the alignment line 2, the back side is printed in thetransfer printing region in parallel to and synchronously with theA-web. The B-web, further, runs parallel to the A-web over a looptractor 6/2, an underpressure brake 7/2 and through the friction drive 8of the fixing station again. Subsequently, it is supplied to a paperoutput, for example a stacker, or some other paper post-processingmeans.

A band store 11 in the form of a loop tractor is arranged between thereturn of the A-web and the redelivery of the web into the positivedrive 3 as the B-web, being arranged following the turning means 10 inthe paper conveying direction. In the arrangement described here, thisloop corresponds to the web store between two positive drives whosefunction was initially described. The stored content of the loop, thus,does not summarily change without regulation. The store is merely neededto compensate for tolerances and for forms synchronization giveninsertion of forms having different lengths.

The friction drive 8 is formed in the printer by the fixing drum 8/1 andpressure roller 8/2 and has the job of fixing the toner images on therecording medium 1. The driven fixing drum 8/1 is therefore heated. Theentrained pressure roller 8/2 is pressed against the fixing drum. Thepaper web is pressed, heated and driven in a fixing gap 9 between thetwo rollers. The web thereby shrinks in a longitudinal and a transversedirection due to loss of moisture. This means that the spacings betweenthe form elements (such as forms, or perforation holes) become smaller.It follows therefrom that, after the return, the B-web exits thepositive drive 3 with a lower web speed than the A-web.

Elements of the Regulating Means

The regulating means for the positionally exact synchronization of theparallel running of the recording medium webs 4, 5 can, according to theillustration of FIG. 6, be subdivided into the following assemblies.

Loop Tractor Assembly

It is composed of the loop-drawing unit 6 composed of two loop tractors6/1, 6/2 allocated to the respective web 4 and 5 that each comprises aloop tractor angle sensor 12, a spring mechanism 13 for the loop tractor7 and an adjustment means 14 for the loop tractor torque. A means forcoupling the two loop tractors is not shown.

Function Region: Underpressure Brake

It is composed of a means 15 for generating underpressure, for example asuction pump, that is in communication with an underpressure valve and acontrol assembly 16 composed of two separately controllable valves 16/1,16/2 and that is coupled to the actual underpressure brake 7 composed oftwo separate glide surfaces 7/1, 7/2 with suction holes.

Fixing Region

It is composed of the fixing drum 8/1, a drive 17 in the form of anelectric motor for the fixing drum 8/1, of the pressure roller 8/2 aswell as a pivoting mechanism 18 for the pressure roller 8/2 composed oftwo cams coupled with a drive 19 via a rotational axis that engage atthe shaft of the pressure roller 8/2 via lever elements.

Electronics

Included here is the actual control electronics 20 composed amicroprocessor-controlled arrangement constructed in the usual way thatis in communication via bus lines with a power electronics 21 for thedrive of the fixing station, the drive 19 of the pressure roller and thevalves 16/1, 16/2 of the brake and is also in communication via a busline with a control electronics 22 constructed in the usual way for adrive of the positive drive 3 (or caterpillar) of the transfer printingstation. The control electronics 20 is also coupled via lines with therotational angle sensors 12 of the loop tractors 6 and is incommunication via a bus line 24 with the device controller of theprinter. The structure thereof is known from the published applicationWO 94/27193.

Input quantities for the control are supplied to the control electronics20 via the bus or control lines 24 from the surroundings (for example,the device controller) and, via the control 22, from the drive 23 of theconveyor caterpillars in the transfer printing station.

Various Embodiments of the Loop Tractor

Dependent on the desired, different function options of the controlmeans that are described later, various embodiments of the loop tractorshown in FIGS. 8-12 can be utilized:

Basic Structure (FIG. 8)

The side-by-side loop tractors 6/1, 6/2 are deflected with arespectively separate spring 13/1, 13/2 that engage at excursionelements 25 via link levers 30. The initial angular position of the linklevers 30 influences the modification of the restoring moment (M) of theloop tractors with the loop tractor angle (β). At the other side, therespective spring 13/1, 13/2 is in communication with a cable 31. Thiscable 31 is attached to a roll-up means 32. A shaft 35 is turned herevia a hand crank 33 and worm gear pair 34. The roll-up means can workcontinuously or only in a defined angular range. The two cable rollers36/1, 36/2 as well as a pointer 37 of a force adjustment scale 38 areseated on this shaft 35.

Due to the specific design of the roll-up means 32, the restoring momentbetween the two loop tractors 6/1, 6/2 can be adjusted.

Symmetrical Embodiment

Given a symmetrical embodiment according to FIG. 9a, the generatedrestoring moments M of the two loop tractors 6/1, 6/2 are the same inboth webs A, B. This is advantageous when the paper webs have the samestructure and there is no tendency that one web basically tends toward alarger loop than the other. The characteristics (abscissa β, ordinate M)of the restoring moments additionally shown are the same in each of theadjustment positions (I, II of the scale in FIGS. 9b and 9c) for bothloop tractors 6/1, 6/2. Link levers can also be utilized instead of thecable rollers 36/1, 36/2.

Asymmetrical Embodiments

Asymmetrical embodiments are advantageous when the webs behavedifferently with predictable direction. This can be opposed here withdifferent forces and force characteristics.

Lead of a Page

When the cable 31 (FIG. 8) is shortened at only one loop tractor, adifference in the two moment characteristics arises. Given an otherwisesymmetrical roll-up behavior, this difference remains the same over allforce settings. Given asymmetrical arrangements, and intentional offsetbetween loop tractor A and B is generated with the cable length.

Different Roll-Up Behavior

Different Diameters of the Cable Rollers (FIG. 10a)

What is achieved with this arrangement is that a difference of the twomoment characteristics changes linearly via the adjustment. The specialcase is shown wherein the two characteristics coincide at the adjustmentposition I in FIG. 10b. This effect can also be achieved with linklevers of different lengths given a non-racing adjustment.

Other Forms of Roll-Up Cams (FIGS. 11a, b and c, 12a, b and c)

When the adjustment of the moment characteristics or the differencebetween the moment characteristics should change non-linearly, differentroll-up cams can be utilized. These are generally different cam shapes,with the special cases: eccentric, ellipse, helix.

Lever Articulations (FIGS. 11a, b and c, A-page)

Levers 39 to which the cable 31 is hinged can also be utilized insteadof the cable rollers 36. It is possible to achieve different andnon-linear adjustment characteristics on the basis of differentcorrection angles.

Different Spring Characteristic (FIGS. 12a, b and c)

The slopes of the moment characteristics is differently configured dueto different spring ratings of the springs 13/1, 13/2. The difference inthe slop of the characteristic remains the same over different forcesettings. Springs having different prestress act like the variation ofthe cable length between the A-side and B-side.

Combinations

Combinations of the embodiments that have been presented are alsopossible. Deviating, thus, from the previously described adjustmentmeans, two adjustment means can also be utilized for the adjustment ofthe two loop tractor characteristics. With separate adjustment means forthe loop tractors, these can be adjusted independently of one another.With a composite adjustment means composed, for example, of twogenerally acting devices, thus, the force level of the two sides can beset in the same sense, on the one hand, and, on the other hand, theforce difference between the two loop tractors.

Motor Adjustment

The mechanical adjustment via cranks and worm gear pairs can also ensueautomatically (with, for example, an electric motor). This is also trueof the separate adjustment.

The printer itself can determine the rated values for the automaticadjustment of the loop tractor forces. The setting of the loop tractorforces can ensue once upon insertion of the paper or can additionallyensue dynamically during operation. The relevant measured quantitiestherefor are: paper width, position of the loop tractors, position ofthe web edge following the loop tractor or the slippage of the webs inthe following fixing station.

Function of the Regulation

The function of the regulation is explained below with reference to thevarious positions of the loop tractors that are shown in FIG. 7 andsensed via the rotational angle sensors 12, whereby each loop tractorcomprises a deflection element 25 pivotable around a rotational axistogether with appertaining deflection springs 13/1, 13/2 (FIG. 8). Eachof the loop tractors 6/1 and 6/2 thereby swivels around a rotationalaxis 28 between an upper mechanical detent 26 and a lower mechanicaldetent 27. Its current position is dependent on the loop length releasedby the paper webs and, thus, on the content of the band store or,respectively, on the stored band length. Thereby denoting are: O, theupper error region; R, the working region; U, the lower error region;RL, the repetitive error of the loop length regulation; MA, the averageof the current loop tractor position; and Mr, the middle of the workingregion of the loop tractor.

Loop Length Regulation

The manipulated variable is regulated to its rated value by varying thespeed of the fixing drum 8/1 via the control electronics 20. The averageMA (FIG. 7) of the current loop tractor positions 6/1, 6/2 is themanipulated variable. The rated value is, for example, the middle MR ofthe working region of the loop tractors. The repetitive error of theloop length regulation RL is thus regulated toward zero.

This regulation differs as a result thereof from the drive speedregulation discussed initially in conjunction with two friction drivesin series. The present regulation means does not regulate to a parameterof one web but to the status of the webs relative to one another.

Loop Difference Regulation

The difference of the loop tractor positions in the A-web 6/1 and theB-web 6/2 (repetitive error RD of the loop difference regulation (FIG.7)) is regulated toward zero with the loop difference regulation. Givenemployment of a purely proportional control algorithm, a lastingrepetitive error can remain. This is potentially desired since thesupport of the regulation by the loop tractors can thereby ensue.

The two underpressure brakes 7/1, 7/2 serve as actuators for the loopdifference regulation. The loop difference regulation supplies the ratedvalues for the lower-ranking pressure regulation of the respectiveunderpressure brake via the valves 16/1, 16/2. As a result thereof, theslippage of the A- and B-webs in the fixing gap 9 between the rollers8/1 and 8/2 is varied relative to one another.

The braking forces are varied proceeding from, for example, standardsettings or, respectively, standard values for the underpressure thatare stored in a memory of the control electronics 20 in the form oftables. Dependent on the direction and size of the difference of theloop tractor positions, the braking force is increased proportionally inthe one web and reduced proportionally in the other web.

The symmetrical variation of braking force described here can also ensuein some other way; for example, proceeding from low braking forces forboth webs, the braking force can be increased only in the web in which arelatively greater slippage is to be achieved.

Modifications and Expansions of the Regulation

Isodirectional change of the paper braking force of the underpressurebrake is one modification. Up to now, the underpressure brakes 7/1, 7/2were used by the loop difference regulation in order to vary the brakingforces transmitted onto the paper webs 4, 5 web-specific and oppositelydirected. However, the underpressure brakes 7/1, 7/2 can also be usedfor the loop length regulation. When, for example, the two paper webs 4,5 exhibit extremely high slippage in the fixing drum gap 9, the standardstarting values for the rated underpressure can be isodirectionallyreduced on both webs by the loop length regulation. This can ensuemanually or automatically by calling reduced standard values from thetable memory of the control electronics 20.

Regulation of the Pressing Power

The pressing power is the force with which the pressure roller 8/2 ispressed against the fixing drum 8/1. It greatly influences therelationship between the paper tensing force and the slippage of thewebs in the fixing drum gap 9. A greater slippage of the paper webs 4, 5is achieved by lower pressing power given the same paper tensing force.

In order to preclude tearing of the paper, the tensile forces in thepaper webs must be limited. The forces limited in this way at theunderpressure brake and at the loop tractor may, given papers havingextremely low slip behavior, not be in the position to govern the loopdifferences. The loop tractors move farther and farther apart. In orderto achieve a greater slip difference with the available difference inforce, it can be necessary to reduce the pressing power of the pressureroller against the fixing drum.

When, for example, the loop difference regulation in the described caseis not in the position of compensating the loop difference withallowable tensing forces, it reduces the pressing power via the pivotmechanism 18 of the pressure roller by turning the cam via the motor 19.By contrast, the pressing power is increased given occurrence of highslip values. The pressing power, however, cannot be arbitrarily reducedsince the fixing is no longer adequate given too low a pressing power. Ahigh pressing power has a beneficial influence on the fixing of theprinting format.

Synchronization Stop

When the two paper webs 4, 5 can no longer be kept within predeterminedlimits by the mechanical and control-oriented measures for varying theslippage, a synchronization stop is automatically generated.

This, for example, is the case when the regulation of the loopdifferences can no longer limit the loop difference even given minimalpressing power of the pressure roller. One loop tractor then swivelsinto an error region that is recognized by the corresponding anglesensor 12 and reported to the control electronics 20. This stops theprinter via the device controller. The conditions therefor areindependently recognized by the printer by logical evaluation of thesensor signals and can be defined by inputting and storing correspondinglimit values or, respectively, conditions in a memory area of thecontrol electronics 20. The printer stops automatically in thesynchronization stop; both loop tractors are pulled back into theparallel starting position, for example automatically by calling thecorresponding standard start values or by displacing and aligning thewebs relative to one another manually with the assistance of thealignment line 2 in the transfer printing region; and the printerautomatically restarts. This procedure can cyclically repeat. It can bebeneficial to employ reduced values instead of employing standardsettings in the restart following a synchronization stop. When a paperexhibits such slippage that a synchronization stop occurs once, it isprobable that this will cyclically repeat. The pressing power shouldalready be reduced at the restart in order to then keep the printingcycle as long as possible. Dependent on the device design, the cyclicalrepetition of the synchronization stop can replace the entire loopdifference regulation.

Varying the Lubrication of the Fixing Drum

The lubrication of the fixing drum with parting oil that is standard inthermal fixing stations in order to avoid offset print effects due totoner adhering to the fixing drum influences the friction relationshipsbetween the paper web and the fixing drum in the fixing gap. Greaterlubrication produces higher slip values given unmodified forcerelationships. When a paper is processed and the slip behavior thereoflies beyond the processable range with the start parameters of theprinter, additional influence can be taken via the lubrication of thefixing drum.

The oiling of the fixing drum is usually utilized for improving thetoner release properties of the oiled drum. Oiling stations whose amountof lubrication can be controlled are used therefor, as is standard inelectrophotography. It is possible to control the oil flow in such anoiling station via the control electronics 20 and to thus influence theslippage.

Progressive Loop Tractor Force

In the arrangement described up to now, the braking or, respectively,tensing forces in the paper webs are only actively generated by theunderpressure brake 7. In addition to the underpressure brake, however,there is also the possibility of introducing tensing forces into thepaper webs with the loop tractors.

The function of the underpressure brake and total loop differenceregulation can be supported or completely taken over by a specificarrangement of the loop tractor mechanism.

Let this arrangement be called progressive loop tractor force here.

The control algorithm of the loop difference regulation fundamentallycontains the function that a relatively higher tensing force isgenerated in the web whose loop tractor resides relatively lower.

Given the progressive loop tractor force, the spring mechanism of theloop tractors is designed such that the loop tractor that is pulledrelatively deeper down introduces a relatively higher tensing force intothe respective paper web than the other. This force difference mustincrease with increasing angle difference.

This demand can be met, for example, by different spring arrangements asdescribed in conjunction with FIGS. 8 through 12.

Isodirectional Change of the Paper Tensing Force with the Loop Tractors

The loop tractor can assume further functions in addition to itscontrol-oriented function. By deflecting the web around the looptractor, this stabilizes and steers further running of the web.Respectively adapted paper traction forces are required here fordifferent web qualities and web widths. This adaptation can ensue via amanual adjustment mechanism, as was likewise described in conjunctionwith FIGS. 8 through 12.

When the loop difference regulation is supported or replaced by aprogressive loop tractor force, the loop length regulation canisodirectionally vary the paper tensing forces with the loop tractors.This can replace the manual setting. Further, the possibilities of theregulation can thus be expanded.

When, for example, the slip of the two paper webs is inadmissibly highat the fixing drum, the tensing force can be isodirectionally reduced inboth paper webs. This enables the loop length regulation via a shift ofthe rated value of the regulation. (It is standard for the rated valueto lie in the middle of the working range of the loop tractors).

Mechanical Actuation of the Underpressure Brake

The loop difference regulation can also be mechanically realized. Forexample, the actuators of the underpressure brakes 7/1, 7/2 (forexample, underpressure valves 16/1, 16/2) are thereby mechanicallycoupled with the loop tractors. The control relationships andproportionalities can then also be realized, for example, via roddingarrangements.

A Fixed Loop Tractor

The loop length regulation regulates the average MA of the two currentloop tractor positions (FIG. 7) to its rated value. The allowablecontrolled difference for the loop difference regulation is maximized bythis procedure. When this is not urgent, the loop length regulation canalso regulate to only one of the loop tractors 6/1, 6/2. In the simplestarrangement, for example, this regulation can be a two-point control.

As already described, the second loop tractor is then regulated relativeto the first.

Processing a Wide Paper Web

The printer device in which the inventive control means is employed hasa basic structure as disclosed by the published application WO 94/27193.The printer device can thus be operated both in two-web as well as inone-web mode. This both with webs having the widths the same as those ofthe two-web mode as well as with a web width across the entire width ofthe two, individual paper webs.

For the participating units, this means, in detail:

Positive Drive

The conveyor caterpillars for the paper conveying in the transferprinting region can be matched to the respective web width. This bothfor two as well as for one web.

Loop Tractors

The two loop tractors are mechanically coupled in one-web mode and actlike a continuous loop tractor. As a result of the coupling, the currentpositions of the loop tractors coincide. Their average value is thusalso identical to their current position. This coupling can be monitoredby a sensor, for example for reasons of dependability.

Underpressure Brakes

The effective width of the underpressure brakes can be set via a widthadjustment, as is standard in single-web electrographic printer devicesthat are suitable for printing different band widths. A continuouslywide web can also operated with it.

Fixing Station

Neither the fixing drum nor the pressure roller are divided in theillustrated thermal fixing means. This also applies given the employmentof a flash fixing means or of a projector fixing means. Such fixingstations are thus suitable for single-web mode which is unmodified. Thereturn, the turning means and the loop of the return are not traversedin single-web mode.

Processing Two Independent Paper Webs

The invention was described with reference to a web configuration in theprinter wherein the recording medium is first printed on the front side,then turned over and returned and then printed on its back side. Withoutmodification of its structure, the regulation is also in the position,analogously, of regulating the synchronous paper running of two separatepaper webs that traverse the entire printer in parallel according to thepublished publication WO 94/27193.

Self-Learning Control Algorithm

The reactions of a rigid control are more or less appropriate dependenton the nature of the printing material. Self-learning controls thatoptimize their control behavior dependent on the printing material andenvironmental conditions are advantageous here. To this end, theparameters of printing material and environmental conditions can beinput into the control means via an input device or the control meansindependently acquires the parameters via corresponding sensors. These,for example, can be standard sensors for sensing the thickness of theprinting material, for acquiring its surface structure, the ambienttemperature, the humidity, etc. It is also possible to identify theprinting material with, for example, a bar code which may be read.

Error Recognition

Data of the current operating condition are measured at variouslocations of the printer for the loop regulation. For example, dataabout the slip behavior of the paper, about content and rate of changeof the paper store, etc., are thus available.

Errors of the machine can be recognized and handled beyond previouspossibilities via limit value and plausibility checks as well as viacombinatorial error analyses of parameters with the assistance of amonitoring arrangement allocated to the regulating means or the devicecontroller. The monitoring function can also be assumed by the controlelectronics itself. A person skilled in the art is familiar with howsuch a monitoring arrangement is to be constructed in circuit-orientedterms.

Further Possibility for Loop Difference Regulation

As explained in conjunction with the loop difference regulation, the twounderpressure brakes 7/1 and 7/2 serve as actuators for introducing theweb-specific tensing forces into the respective paper web A or B. It hasnow turned out that an arrangement for page regulation of the paperrunning (edge regulation) of a paper web that is basically known fromU.S. Pat. 5,323,944 and shown in FIG. 13 is especially well-suited as anactuator for introducing the web-specific tensing forces into therespective paper web A or B. The arrangement can be employed as a soleactuator or can be employed in combination with another actuator thatinfluences the web-specific tensing forces, for example theunderpressure brakes 7/1 and 7/2. In a combination, it is especiallysuited for fine control.

As shown in FIG. 13, the arrangement acts on the fixing drum 201 that isconstructed in conformity with the fixing drum 8/1 of FIG. 6. A pressureroller 205 corresponding to the pressure roller 8/2 of FIG. 6 can beswivelled in against and away from the fixing drum. The pressure roller205 is seated on two lateral bearing elements 206. The bearing elements206 are in turn arranged in the frame of the printer device swivellablearound a stationary rotational axis. Two eccentric disks 209 that can beturned via an electric motor 208 and that lie against guide projections210 (rotatable rollers) of the bearing elements 206 are provided forswivelling the pressure roller in against and away from the fixing drum201 that acts as a counter-roller. Two restoring springs 211 laterallyengaging at the bearing elements 206 pull the bearing elements 206against the eccentric disks 209 via the guide projections 210.

The eccentric disks 209 are respectively arranged in an end of alever-like rocker 212. These rockers are seated rotatable around astationary rocker axis 213 parallel to the pressure roller axis. Springelements 218 in the form of coil springs are hooked to a side of therockers 212 lying opposite the eccentric disk. The other end of the coilsprings 218 is connected to a cable or a chain 217 that is respectivelyguided around a stationary deflection roller 215. The free cable orchain ends are secured to a first end of an adjusting lever 214pivotable around a symmetry axis 216. The effective direction of thespring elements 218 directed perpendicularly to the pressure roller axisis deflected by the force deflection means fashioned as a cable or chain217 and as a deflection roller 215. The effective direction thencorresponds to the swivelling direction 204 of the adjusting lever 214indicated by an arrow. This swivelling direction 204 is directedparallel to the pressure roller axis. As a result of this arrangement ofthe spring elements 218, these exert a tensile force on the rockers 212that is converted such by the rockers 212 in a pressing power that thepressure roller 205 is pressed against the fixing drum 201. For limitingthe range of swing of the rockers 212, adjustable detents 219 arearranged in the bearing region of the eccentric disks 209.

The spring power of the spring elements 218 is noticeably greater thanthe spring power of the restoring springs 211 at the pressure roller205. When pressed against the pressure roller 205, the rockers 212 arepivoted away from the detents 219. According to their rotated position,the eccentric disks 209 press the pressure roller 205 against the fixingdrum 201. The pressing power is thereby essentially defined by thespring power of the spring elements 218 in combination with thegeometrical structure of the rocker 212 and the rotated position of theeccentric disk 209.

The actuator 220 is composed of a spindle 225 directed in the effectivedirection of the spring elements 218, of a spindle nut 223 and of aspindle nut claw 222. The spindle 225 is coupled to a stepping motor 226that can be controlled proceeding from the control unit 21 (see FIG. 6).Upon rotation of the spindle 225, the spindle nut 223 is displaced inlongitudinal direction of the spindle 225 and, dependent on theexcursion of the pivoted lever 214, a corresponding pressing power isthus exerted onto the paper webs A or B (not shown here) guided betweenthe fixing drum 201 and the pressure roller 205. When the one spring 218is tensed by pivoting the pivoted lever 214, the pressing power isincreased in, for example, the region of the B-web and is reduced in theregion of the A-web due to relaxation of the corresponding, other spring218. As a result, the slippage is increased in the A-web and reduced inthe region of the B-web.

A difference in slip of the A-web and B-web can already be generated asa result of slightly unequal pressing powers with the assistance of thepressing power adjustment mechanism. The A-web is thereby oppositelystressed by the same pressing power by which the B-web is relieved.

Particularly given paper grades that have larger holes or that, due totheir quality, cannot be regulated even with maximally possibledifference in underpressure, the opposed adjustment of the pressingpowers is an important alternative.

Modifications and Expansion of the Regulation

The use of the pressing power adjustment mechanism is to be preferredover the above-described regulation of the pressing power since theinfluence on the difference in slip is greater due to opposed adjustmentof the forces.

In particular, the negative influence on the fixing quality is lowersince the opposed reduction of the pressing power of the A-web turns outlower than the simultaneous reduction of pressing power on both webswhen the pivoted cam 18 (FIG. 6) is pivoted away. When the pivoted cam18 is pivoted away, the slip of both paper webs is increased and effectsa difference in slip only indirectly via the use of the underpressurecontrol. A web-specific variation of the pressing powers, by contrast,is possible with the assistance of the pressing power adjustmentmechanism.

Papers with large hole areas and other critical papers (recycled paper,etc.) potentially require frequent synchronization stops solely with theunderpressure regulation without employment of the pressing poweradjustment mechanism. In view of the printer performance, however, suchstops are to be avoided insofar as possible.

The adjustment of the loop tractor force requires an operatorintervention. Each such intervention should be avoided if at allpossible, this being promoted by the use of the web specific pressingpower adjustment.

The use of the opposed pressing power regulation on the one hand and ofthe underpressure regulation or, respectively, loop tractor force on theother hand can basically be arbitrarily combined. With which papers andbeginning at which point the respective regulation should be utilizedindependent of material and function

An example of an electrographic printer device is shown in FIG. 14,including an intermediate carrier 111, a charging device 112, acharacter generator 113, a developer station 114, a transfer printingstation 115, a cleaning station 116 and a discharging means 117. Afixing station 118 follows the transfer printing station 115 and has aheated fixing drum 119, and a pressure roller 120. A stacker 122 for therecording medium 110 is provided with delivery rollers 124. A conveyor125 moves the recording medium through the printer and includes driverollers 127 and a deflector 128.

Although other modifications and changes may be suggested by thoseskilled in the art, it is the intention of the inventor to embody withinthe patent warranted hereon all changes and modifications as reasonablyand properly come within the scope of his contribution to the art.

We claim:
 1. A device for transporting recording medium webs in anelectrographic printer device, comprising:a drive means for positivelydriving the recording medium webs in common, a first function regionthrough which the recording medium webs are passed in parallelside-by-side, a second function region through which the recordingmedium webs are then supplied in parallel side-by-side, a friction drivein common with said first function region and said second functionregion, a surface speed of a surface of the friction drive driving therecording medium webs is undifferentiated for the recording medium webs,a regulating means for controlling running of the recording medium websby slippage of the friction drive of each individual one of saidrecording medium webs, said regulating means including:an acquisitionmeans for acquiring a relative displacement in a conveying direction ofthe recording medium webs relative to one another in a region betweensaid first and second function regions; adjustment means for adjustingthe slippage of each individual one of said recording medium webs in thefriction drive of the second function region; control means forcompensating the relative displacement that are coupled to theacquisition means and the adjustment means;at least one band store forstoring the recording medium webs, and a sensor acquiring a fillingcondition of said at least one band store.
 2. A device according toclaim 1, wherein said acquisition means includes loop tractors withsensors which acquire rotated positions of said loop tractors, said looptractors being allocated to the recording medium webs.
 3. A deviceaccording to claim 2, further comprising: loop-forming units whichdeflect the recording medium webs with an adjustable deflection forcedependent on a rotated position of said loop-forming units.
 4. A deviceaccording to claim 3, wherein said loop-forming units include deflectionelements with appertaining deflection springs that engage at therecording medium webs and are pivotable around a rotational axis, thedeflection springs being coupled to a tensing means for setting springprestress.
 5. A device according to claim 2, wherein said at least oneband store includes a plurality of band stores and wherein saidregulating means includesa first function group that controls content ofthe band stores that influences content of the band stores of therecording medium webs in a same sense, and a second function group thatcontrols a difference of the contents of the band stores that,oppositely influences the contents of the band stores.
 6. A deviceaccording to claim 2, further comprising: sensors sensing markings onthe recording medium webs.
 7. A device according to claim 2, furthercomprising:a brake arranged preceding the friction drive in a recordingmedium conveying direction; and means for regulating braking power onthe recording medium web.
 8. A device according to claim 7, wherein saidbrake includes a glide surface with suction openings accepting therecording medium webs, said suction openings being allocated to each ofthe recording medium webs, said glide surface being coupled to a meansfor generating an adjustable underpressure.
 9. A device according toclaim 1, wherein said electrographic printer device includes a transferprinting region, wherein said first function region being a transferprinting station and said second function region being a fixing station.10. A device according to claim 1, wherein said second function regionincludes a fixing drum with an appertaining pressure roller that pressesthe recording medium webs against the fixing drum, at least one of saidfixing drum and said pressure roller being heated and motor-driven. 11.A device according to claim 1, further comprising:a controllable devicefor setting pressing power on the recording medium webs.
 12. A deviceaccording to claim 11, wherein said friction drive includes a driveroller, and further comprising:a movably seated pressure roller pressingthe recording medium webs against said drive roller of the frictiondrive and a force adjustment mechanism coupled to said movably seatedpressure roller to web-specifically vary pressing power of said movablyseated pressure roller in a region of the recording medium webs.
 13. Adevice according to claim 12, further comprising:spring elements, asetting means coupled to said spring elements, said setting means havinga zero position, and respective lateral bearing element of the pressureroller coupled to said spring elements such that said lateral bearingelements press the pressure roller in force-compensating fashion againstsaid drive roller in the zero position of the setting means,transmission of force to the bearing elements that is dependent on asetting position then ensues by excursion of the setting means out ofthe zero position.
 14. A device according to claim 10, furthercomprising:means for controlling variation of coefficient of friction ofsaid fixing drum and said pressure roller.
 15. A device according toclaim 14, wherein said means for controlling the variation of thecoefficient of friction includes means for controlling delivery ofparting oil.
 16. A device according to claim 9, wherein said fixingstation includes a flash fixing means.
 17. A device according to claim9, wherein said fixing station includes a projector fixing means.
 18. Adevice according to claim 1, further comprising:means allocated to theregulating means by which a synchronization stop is triggered givenupward transgression of a predetermined range of control, during whichsynchronization stop a synchronization of parallel running of therecording medium webs can ensue by relative displacement of therecording medium webs into a synchronous position.
 19. An electrographicprinter device for single-sided or both-sided printing of a band-shapedrecording medium, comprising:an intermediate carrier for generatingtoner images allocated to at least one of a front side and a back sideof the recording medium; a transfer printing station havinga firsttransfer printing region for transfer of a first toner image onto afront side region of the recording medium and a second transfer printingregion lying adjacent said first transfer printing region for transferof a further toner image onto the front side region or a back sideregion of the recording medium, as well as a conveyor means thatpositively drives the recording medium in the first and second transferprinting regions; a turning means for turning the recording medium over;a fixing station following the transfer printing station in a conveyingdirection of the recording medium havingan allocated friction drive forthe recording medium, the recording medium, in a first recording mediumweb proceeding from a delivery region, being conducted via the firsttransfer printing region to the fixing station and, turned over by theturning means as needed for printing the back side region, beingconducted therefrom to the second transfer printing region and beingconducted again through the fixing station in a second recording mediumweb and a drive means for positively driving the recording medium websin common, a first function region through which the recording mediumwebs are passed in parallel side-by-side, a second function regionthrough which the recording medium webs are then supplied in parallelside-by-side, a friction drive in common with said first function regionand said second function region, a surface speed of a surface of thefriction drive driving the recording medium webs is undifferentiated forthe recording medium webs, a regulating means for controlling running ofthe recording medium webs by slippage of the friction drive of eachindividual recording medium web, said regulating means including:anacquisition means for acquiring a relative displacement in a conveyingdirection of the recording medium webs relative to one another in aregion between said first and second function regions; adjustment meansfor adjusting the slippage of each individual recording medium web inthe friction drive of the second function region; control means forcompensating the relative displacement that are coupled to theacquisition means and the adjustment means; at least one band store forstoring the recording medium, and a sensor acquiring a filling conditionof said at least one band store.
 20. A method for transporting recordingmedium webs in an electrographic printer device, comprising the stepsof:positively driving the recording medium webs in common via a drivemeans, passing the recording medium webs through a first function regionin parallel side-by-side, supplying the recording medium webs inparallel side-by-side to a second function region with a common frictiondrive, surface speed of a surface of the friction drive driving therecording medium webs cannot be differentiated for the recording mediumwebs, acquiring a relative displacement in a conveying direction of therecording medium webs relative to one another in a region between atransfer printing region and a fixing station; controlling slippage ofthe friction drive in the conveying direction of each individualrecording medium web until the relative displacement falls below aprescribable value.